A low coming from New South Wales in Australia will start to make its way over the South Island today before covering the North Island with heavy rain on Wednesday.
WeatherWatch.co.nz chief analyst Philip Duncan said a large high lay out to the east of the country and a developing low lay to the west, which created a passage for a "very humid" northerly wind down the country.
"So that should help boost the temperatures right up, possibly over 30 degrees in Hawkes Bay," Mr Duncan said.
And even though most of the country should prepare for rain, particularly the North Island, Mr Duncan said it would be far from cold.
"It looks like it's going to be a hot, humid and muggy week, even if it is a bit wet."
Up until the weekend, most of the country would be covered by the slow-moving low, Mr Duncan said.
"I think it will clear up on Friday, maybe with a few showers hanging around, but I think it will clear up then," he said.
"But possibly another front could move past just after that low leaves."
NZHerald